BpmCalculator provides interval math (60000 / bpm) and volume
clamping (0.0-1.0). AudioEngine drives AudioTrack on a dedicated
HandlerThread, scheduling beeps via postDelayed for battery-
efficient background playback.
Audio focus is intentionally never requested so beeps play
alongside other apps without ducking (US-05).
Initial project structure with manifest configured for foreground
audio service, AudioTrack-based playback, and background operation.
Includes Gradle wrapper, dependency catalog, placeholder icons,
and build instructions for Arch Linux.